The present invention introduces a distributed protocol for measurement of the channel state information of multiple transmission/reception (Tx/Rx) modes (defined by frequency channels or antenna patterns) on all wireless links in a multi-hop wireless network. The protocol does not need to be integrated with the Medium Access Control (MAC) protocol but can operate at a higher layer (e.g. network layer) of the OSI protocol stack. This makes the protocol general and independent of the wireless technology being used.
Currently there exist no solutions that address the wireless channel state measurement problem in a general multi-mode, multi-hop wireless network environment.
Channel state measurement mechanisms for cellular networks are centralized and perform measurements on individual links of a star topology (between a single base station and multiple mobile terminals) and on a single mode (fixed frequency channel and antenna pattern) after resources have been allocated to a link. Furthermore, channel state measurements are typically integrated with the MAC protocol and are specific to the wireless technology being used. Recent research has focused on channel state measurement algorithms for multi-channel wireless systems (S. Guha, K. Muagala, and S. Sarkar, “Optimizing transmission rate in wireless channels using adaptive probes”, in Proceedings of SIGMETRICS/Perfrormance, 2006.-A.˜Sabharwal and A.˜Khoshnevis and E.˜Knightly, “Opportunistic Spectral Usage: Bounds and a Multi-Band {CSMA/CA} Protocol”, IEEE/ACM Transactions on Networking, June, 2007.-N. Chang and M. Liu, “Optimal channel probing and transmission scheduling for opportunistic spectrum access”, in Proceedings of ACM International Conference on Mobile Computing and Networking (MobiCom), Montreal, Canada, 2007.-A. Gopalan, C. Caramanis, and S. Shakkotai, “On wireless scheduling with partial channel-state information”, in Proceedings of the 45th Allerton Conference on Communication, Control and Computing, Urbana, Ill., 2007.-C. Li and M. J. Neely, “Energy-optimal scheduling with dynamic channel acquisition in wireless downlinks”, in Proceedings of 46th IEEE Conference on Decision and Control, 2007.) These papers again focus on the star topology case where a single transmitter (base station) needs to acquire channel state information of a number of time varying channels. These techniques cannot be applied to distributed multi-hop wireless networks. In addition, they only focus on algorithmic aspects such as formulating optimal probing policies rather than specifying protocols that can realize such policies.
IEEE 802.11-based wireless networks can operate in both star-topology (WLAN) and distributed multi-hop (“mesh”) configurations. Such networks implement channel state acquisition at the network layer (above the 802.11 MAC) by sending broadcast probe packets that measure Received Signal Strength (RSS) at each receiver. The following References: J. Padhye, S. Agarwal, V. Padmanabhan, L. Qiu, A. Rao, and B. Zill. “Estimation of Link Interference in Static Multi-hop Wireless Networks.” In Proc. ACM Internet Measurement Conference (IMC), Berkeley, Calif., USA, October 2005.-D. Aguayo, J. Bicket, S. Biswas, G. Judd, and R. Morris. “Link-level Measurements from an 802.11b Mesh Network.” In Proc. ACM SIGCOMM, Portland, Oreg., August 2004.-N. Ahmed, U. Ismail, S. Keshav, and D. Papagiannaki. “Online Estimation of RF Interference.” In Proc. ACM CoNEXT, Madrid, Spain, December 2008.-Y. Li, L. Qiu, Y. Zhang, R. Mahajan, and E. Rozner. “Predictable Performance Optimization for Wireless Networks.” In Proc. ACM SIGCOMM, Seattle, Wash., USA, August 2008. (other references therein) specify channel state acquisition mechanisms for 802.11 multi-hop mesh networks where N nodes send broadcast probe packets sequentially in N cycles. During each cycle a single node sends several broadcast probe packets while the rest of the nodes listen. This results in measuring the channel state (RSS) of all links in the network using O(N) measurements. However, these solutions are specific to single-mode channel state measurements which use transmissions on a single frequency channel and only use omni-mode for antenna transmission. In multi-mode wireless networks, nodes need to coordinate to tune on the same Tx-Rx mode at the same time instant, which makes the channel state measurement problem much harder.